Most of these small diameter clutches (Tilton/Quartermaster) are hard to drive because of the sintered metallic material. If it's that coppery coler, it's going to be hard to modulate regardless of clutch diameter.
I have driven a 5.5" 4-plate with a special lining (designed to slip) and a 5.5" carbon-carbon 3-plate and both were easy to modulate. To the point that having very little inertia wasn't a problem.
If you're replacing the discs, remember that you'll need to ensure the total stack height is the same. If I recall correctly, you can take a 4-disc tilton/quartermaster basket, and make it a 3-disc organic using the .2" thick PTT discs and be really close to the original stack height. I think this would be a sweet setup, and I plan to do a 5.5" version for my car in the future. I was quoted $430 for the 5.5" organic 3-disc pack.
I think super low inertia makes for a really fun car to drive.
Don't forget, you'll need an annular release bearing for most of these clutches.